%0 Clinical Trial %T Complex and monosomal karyotype are distinct cytogenetic entities with an adverse prognostic impact in paediatric acute myeloid leukaemia. A NOPHO-DBH-AML study. %A Bager N %A Juul-Dam KL %A Sandahl JD %A Abrahamsson J %A Beverloo B %A de Bont ESJM %A Ha SY %A Jahnukainen K %A Jónsson ÓG %A Kaspers GL %A Kovalova Z %A Lausen B %A De Moerloose B %A Noren-Nyström U %A Palle J %A Saks K %A Zeller B %A Kjeldsen E %A Hasle H %J Br J Haematol %V 183 %N 4 %D 11 2018 %M 30406946 %F 8.615 %R 10.1111/bjh.15587 %X Data on occurrence, genetic characteristics and prognostic impact of complex and monosomal karyotype (CK/MK) in children with acute myeloid leukaemia (AML) are scarce. We studied CK and MK in a large unselected cohort of childhood AML patients diagnosed and treated according to Nordic Society for Paediatric Haematology and Oncology (NOPHO)-AML protocols 1993-2015. In total, 800 patients with de novo AML were included. CK was found in 122 (15%) and MK in 41 (5%) patients. CK and MK patients were young (median age 2·1 and 3·3 years, respectively) and frequently had FAB M7 morphology (24% and 22%, respectively). Refractory disease was more common in MK patients (15% vs. 4%) and stem cell transplantation in first complete remission was more frequent (32% vs. 19%) compared with non-CK/non-MK patients. CK showed no association with refractory disease but was an independent predictor of an inferior event-free survival (EFS; hazard ratio [HR] 1·43, P = 0·03) and overall survival (OS; HR 1·48, P = 0·01). MK was associated with a poor EFS (HR 1·57, P = 0·03) but did not show an inferior OS compared to non-MK patients (HR 1·14, P = 0·62). In a large paediatric cohort, we characterized AML with non-recurrent abnormal karyotype and unravelled the adverse impact of CK and MK on prognosis.